The aim of this proposed work is to test the hypothesis that prostaglandins of the series (PGE1 and PGE2) induce a state of temporary or transient growth arrest in human diploid fibroblasts (HDF) grown in vitro. The initial mechanism whereby transient growth arrest in induced involves an alteration in fibronectin (hybridoma HFN 7.1). Further, the relationship between an alternation in fibronectin mediated cell adhesion by PGE. This will be tested directly in experiments using a quantitative cellular adhesion assay and in experiments using a monoclonal antibody directed against human fibronectin mediated cell adhesion by PGE and proliferative capacity will be tested in experiments that compare the fluorescence pattern of fibronectin and the ability to progress to S phase in the same cells. Alterations in the regulation of this growth arrested state during aging will be examined by comparing the response of fibroblasts from donors of 29, 59 and 92 years, as well as those from a patient with progeria, to inducers (PGE1 and PGE2) and inhibitors (hydrocortisone) of transient growth arrest. A second aim of this work is to develope quantitative methods to study the roles of other defined medium components in modulating growth arrest in HDF. These methods, multiparameter flow cytometry and cell fusion assays, provide ways to discriminate between those factors that modulate transient growth arrest and those that affect permanent growth arrest. Since most fibroblasts in vivo are not in a state of either continuous proliferation or in a state of terminal growth arrest, an understanding of the mechanisms that govern transient growth arrest in vitro could serve to generate new knowledge about the regulation of fibroblasts in humans.